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Potential human health risk assessment (HRA)

PHASE I LULC

4.7.1. Potential human health risk assessment (HRA)

4.6.3. Elemental analyses

XRD analysis was carried out for three samples (powdered); (i) samples from the central zone, (ii) Boragaon landfill site and (iii) industrial zone to determine the forms in which the HMs are present in the samples. SEM-EDS quantitative analyses were furthermore carried out to determine the morphology and the elemental composition of the sediment samples. Two representative samples (powdered) were chosen; one from the eastern part of the wetland (proximate to the Boragaon landfill) and the other from the western part (industrial zone).

Elemental mapping of the samples was done to determine the weight percentages of the HMs present in those samples.

4.7. Phase II; IV

th

Objective: Understanding the dynamics of heavy

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dose-response, and risk characterization. In the water environment, the metals usually come in contact with the human body through the first two pathways, i.e., via ingestion and dermal adsorption (EPA 2004; Wu et al. 2009; Singh et al. 2018). However, heavy metal exposure in the sediment column takes place through all three pathways. The health risk associated with the water environment can be explained through Eq. 4. 62 and 4. 63, which provides the av- erage daily dosages for heavy metals through different pathways.

𝐢𝐷𝐼𝑖𝑛𝑔 =𝐢𝑀× 𝐼𝑛𝑔𝑅 Γ— 𝐸𝐹 Γ— 𝐸𝐷

𝐡𝑀× 𝐴𝑇 4. 62

πΆπ·πΌπ‘‘π‘’π‘Ÿπ‘š= {𝐢𝑀× 𝑆𝐴 Γ— 𝐾𝑝× 𝐸𝑇 Γ— 𝐸𝐹 Γ— 𝐸𝐷

𝐡𝑀× 𝐴𝑇 } Γ— 10βˆ’3 4. 63

For the sediment column, the average daily dosage of heavy metals can be estimated by computing the following equations (Eq. 4. 64 - 4. 66).

𝐢𝐷𝐼𝑖𝑛𝑔 = {𝐢𝑆𝐸𝐷× 𝐼𝑛𝑔𝑅 Γ— 𝐸𝐹 Γ— 𝐸𝐷

𝐡𝑀× 𝐴𝑇 } Γ— 𝐢𝐹 4. 64

πΆπ·πΌπ‘‘π‘’π‘Ÿπ‘š= {𝐢𝑆𝐸𝐷× 𝑆𝐴 Γ— 𝐴𝐹𝑆𝐸𝐷× 𝐴𝐡𝑆 Γ— 𝐸𝐹 Γ— 𝐸𝐷

𝐡𝑀× 𝐴𝑇 } Γ— 𝐢𝐹 4. 65

πΆπ·πΌπ‘–π‘›β„Ž=𝐢𝑆𝐸𝐷× 𝐸𝐹 Γ— 𝐸𝐷

𝑃𝐸𝐹 Γ— 𝐴𝑇 4. 66

where 𝐢𝐷𝐼𝑖𝑛𝑔 and πΆπ·πΌπ‘‘π‘’π‘Ÿπ‘š indicate the average daily dosage of heavy metals through in- gestion and dermal adsorption, respectively. The other parameters used in the equations have been stated in Table 4. 9 (a and b).

HRA involved estimating carcinogenic (surficial sediment samples) and non-carcinogenic risk exposures (both water and sediment samples) in both adults and children through the bioavailability of the heavy metals. This quantification of risk characterization for non-car- cinogenic risks was accomplished by estimating the Hazard Quotient (HQ) values expressed in Eq. 4. 67 (EPA 1989).

𝐻𝑄 =𝐢𝐷𝐼

𝑅𝑓𝐷 4. 67

where 𝑅𝑓𝐷 indicates the reference dosages for HRA calculation (USEPA 2011) (See Table 4. 10).

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Table 4. 9. Input parameters involved for health risk assessment.

(a) Water Exposure parame- ters

Description Unit

Value

Reference

Adult Child

Cw Heavy metal concentration in

water samples Β΅g L-1

Observed con- centrations

-

IngR Ingestion rate of water L day-1 2.2 - (Wu et al.

2009)

EF Exposure frequency days

year-1

365 - (EPA 2004)

ED Exposure duration Years 70 - (EPA 2004)

Bw Body weight Kg 57.5 (Average

Indian adult) - (USEPA 2011) AT Averaging Time (non–car-

cinogenic) Days 25550 - (DoE 2011)

SA Surface area of skin that con-

tacts soil cm2 5700 - (USEPA 2011)

Kp Dermal permeability coeffi-

cient cm h-1 Metal specific - (EPA 2004)

ET Exposure time h day-1 0.6 - (EPA 2004)

(b) Sediment Exposure parame- ters

Description Unit

Value

Reference Adult Child

CSED Heavy metal concentra-

tion in sediment samples mg kg-1 Observed concentrations

IngR Ingestion rate of sediment mg day-1 100 200 (USEPA 1997, 2011) EF Exposure frequency days year-

1

350* 350* (USEPA 1991,

2011)

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ED Exposure duration Years 24** 6 (USEPA 2011)

BW Body weight Kg 57.5 15 (NFI 2010;

USEPA 2011) AT Averaging Time (non–car-

cinogenic) Days

8760 (356Γ—24)

2190 (356Γ—6)

(USEPA 2011)

CF Conversion factor 1 Γ— 10-6 1 Γ— 10-6 (USEPA 2002)

SA Surface area of skin that

contacts soil cm2 5700 2800 (USEPA 2011)

AFSED Skin adherence factor for

soil mg cm-2 0.07 0.2 (USEPA 2011)

ABS Dermal absorption factor 0.03 (As); 0.001 (for other metals)

(USEPA 2011)

PEF Particle emission factor m3 kg-1 1.36 Γ— 109 1.36 Γ— 109 (USEPA 2002)

*Default exposure frequency for residents assuming a person is out of station for 15 days per year (USEPA 1991).

**Exposure duration is with an assumption that a person lives at one residence for 30 years (0–6 years as a child and 7–30 years as an adult) (USEPA 1991).

(c) Fish Exposure parame- ters

Description Unit

Value

Reference

Adult Child

EDI Estimated daily fish in- take

Β΅g kg-1 day-1

Observed concentrations

Cmetal Heavy metal concentra-

tion in fish samples mg kg-1

DFC Daily fish consumption g day-1 97.2 57.5 (Gupta et al.

2015) WAB Average body weight of

the consumer kg 55.9 32.7 (Gupta et al.

2015)

EF Exposure frequency Days 365 365 (Siddiqui et al.

2019)

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ED Exposure duration Years 70 70 (Siddiqui et al.

2019)

FIR Fish Ingestion rate gpcd 97.2 57.5 (Siddiqui et al.

2019) AT Average exposure time for

noncarcinogenic expo-

sure Days 25550 25550

(Siddiqui et al.

2019)

To estimate the total non-carcinogenic contribution of risk for multiple pathways, a new term called the Hazard Index (HI) was coined (Chang et al. 2014). For estimating the HI val- ues, the law of superposition is valid, and therefore, it helps in evaluating the total non-car- cinogenic risks for multiple metals based on the dose additivity assumption. HI for assessing risk concerning multiple pathways and metals is given in Eq. 4. 68 and 4. 69, respectively.

π»πΌπ‘π‘Žπ‘‘β„Žπ‘€π‘Žπ‘¦= 𝐻𝑄𝑖𝑛𝑔+ π»π‘„π‘‘π‘’π‘Ÿπ‘š+ π»π‘„π‘–π‘›β„Ž 4. 68

π»πΌπ‘šπ‘’π‘‘π‘Žπ‘™= 𝐻𝑄1+ 𝐻𝑄2+ 𝐻𝑄3+ β‹― + π»π‘„π‘š 4. 69

where m signifies the number of heavy metals (in the current investigation, m = 6). HI< 1 represented no significant risk, while HI> 1 indicated the probability of a potential non-car- cinogenic risk, increasing the HI value (USEPA 2002).

The HI is generally employed as a screening tool with regards to the components having a similar target. This is primarily because the HI does not consider the components' interac- tions even though the additivity of the dose essentializes the action of all the components through identical mechanisms. This, in turn, aids in either overestimating or underestimating the health hazards, provided the interactions are less or more, respectively (Wilbur et al.

2004).

The carcinogenic investigation, involving the surficial sediment samples, associates Pb, Cr, and Cd heavy metals and As metalloid, as these compounds are labelled as carcinogenic by the International Agency for Research on Cancer (IARC 2012). Since, As is not considered in the current investigation, the carcinogenic HRA was evaluated associating the heavy met- als; Pb, Cr, and Cd.

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Table 4. 10. Reference dosage values for different heavy metals.

(a) Water (Β΅g/kg/day)

Heavy metal RfDing RfDderm Reference

Cr 3 0.015 (USEPA 2006)

Cd 0.5 0.005 (USEPA 2006)

Fe 300 45 (USEPA 2006)

Mn 20 0.8 (USEPA 2006)

Cu 40 12 (USEPA 2006)

Pb 1.4 0.42 (WHO 2006)

(b) Sediment (mg/kg/day)

Heavy metal RfDing RfDderm RfDinh Reference

Cr 4.00Γ—10-02 8.00Γ—10-03 1.00Γ—10-04 (Giri & Singh 2017) Cd 1.00Γ—10-03 2.50Γ—10-05 1.00Γ—10-05 (Giri & Singh 2017)

Fe 3.00Γ—10-03 7.50Γ—10-05 (Giri & Singh 2017)

Mn 7.00Γ—10-01 1.40Γ—10-01 (Giri & Singh 2017)

Cu 2.40Γ—10-02 9.60Γ—10-04 5.00Γ—10-05 (Giri & Singh 2017) Pb 3.50Γ—10-03 5.25Γ—10-04 1.50Γ—10-04 (Giri & Singh 2017)

(c) Fish (mg/kg/day)

Heavy metal RfD Reference

Cr 3.00Γ—10-03 (USEPA 2010)

Cd 1.00Γ—10-03 (USEPA 2010)

Fe 7.00Γ—10-01 (USEPA 2010)

Mn 1.40Γ—10-01 (USEPA 2010)

Cu 4.00Γ—10-02 (USEPA 2010)

Pb 4.00Γ—10-03 (USEPA 2010)

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The health risk due to carcinogenic metals is expressed as total lifetime cancer risk (LCR), which is also based on the principle of superposition, and is evaluated using Eq. 4. 70 and 4.

71.

πΆπ‘Žπ‘›π‘π‘’π‘Ÿ π‘…π‘–π‘ π‘˜ = 𝐢𝐷𝐼 Γ— 𝐢𝑆𝐹 4. 70

𝐿𝐢𝑅 = βˆ‘πΆπ‘Žπ‘›π‘π‘’π‘Ÿ π‘…π‘–π‘ π‘˜ = πΆπ‘Žπ‘›π‘π‘’π‘Ÿ π‘…π‘–π‘ π‘˜π‘–π‘›π‘”+ πΆπ‘Žπ‘›π‘π‘’π‘Ÿ π‘…π‘–π‘ π‘˜π‘‘π‘’π‘Ÿπ‘š+ πΆπ‘Žπ‘›π‘π‘’π‘Ÿ π‘…π‘–π‘ π‘˜π‘–π‘›β„Ž 4. 71

where cancer risk is estimated for each pathway described by Eq. 4. 64 - 4. 66. CSF (mg kg-1 day-1) indicates the cancer slope factors for each heavy metal; 0.5 for Cr, 6.3 for Cd and 0.0085 for Pb (USEPA 2011). The United States Environmental Protection Agency (USEPA) has marked threshold limits for the cancer risk and the LCR values. The human body's cancer risks have been limited to an acceptable value of 0.0001, while the LCR's tolerable range var- ies from 1.0Γ—10-6 to 1.0Γ—10-4 (USEPA 2011).

Health risk associated with the consumption of fish was assessed by evaluating the esti- mated daily intake (EDI) of fish (Eq. 4. 72), followed by the target hazard quotient (THQ) (Eq.

4. 73) and the total target hazard quotient (TTHQ) (Eq. 4. 74). The assessment was carried out for four different organs (muscle, liver, gill, and skin) of the three fish species (N. no- topterus, C. batrachus, and C. striata) collected from three distinct zones of Deepor Beel. The THQ values provided the non-carcinogenic influence on the human bodies due to the fish in- take; THQ exceeding a unit value indicated potential non-carcinogenic health risk to human beings (USEPA 2000). The cumulative impact exposure to more than one metal was assessed by calculating the arithmetic sum of all the THQ values, which resulted in the total target haz- ard quotient (TTHQ).

𝐸𝐷𝐼 = {𝐷𝐹𝐢 Γ— πΆπ‘šπ‘’π‘‘π‘Žπ‘™

π‘Šπ΄π΅ } 4. 72

𝑇𝐻𝑄 = {𝐸𝐹 Γ— 𝐸𝐷 Γ— 𝐹𝐼𝑅 Γ— πΆπ‘šπ‘’π‘‘π‘Žπ‘™

𝑅𝑓𝐷 Γ— π‘Šπ΄π΅ Γ— 𝐴𝑇 } Γ— 10βˆ’3 4. 73

𝑇𝑇𝐻𝑄 = 𝑇𝐻𝑄𝐻𝑀1+ 𝑇𝐻𝑄𝐻𝑀2+ β‹― + π‘‡π»π‘„π»π‘€π‘š 4. 74

For carcinogenic evaluation due to the consumption of the fish species, two metals la- belled as "possible carcinogenic influence on humans," i.e., Cd and Pb, were considered (alt- hough Cr is also marked; however, USEPA has not published the CSF values yet) (USEPA 2010;

IARC 2012). The lifetime cancer risk (TR) for both the heavy metals was evaluated using the critical slope factor (CSF) values through Eq. 4. 75.

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𝑇𝑅 = {𝐸𝐹 Γ— 𝐸𝐷 Γ— 𝐹𝐼𝑅 Γ— πΆπ‘šπ‘’π‘‘π‘Žπ‘™Γ— 𝐢𝑆𝐹

π‘Šπ΄π΅ Γ— 𝐴𝑇 } Γ— 10βˆ’3 4. 75

All the parameters used in Eq. 4. 72 - 4. 75 have been described with their values in Table 4. 9c. The tolerable limits for TR lie in the range 1.0Γ—10-04 to 1.0Γ—10-06, i.e., the risk of devel- oping cancer over a lifetime lies in the range 1 in 10,000 to 10,00,000.

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